Frequency dependent excursion limiter

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring now to the drawings, FIGS.
1 and 2 illustrate a technique for measuring the maximum safe peak voltage of a loudspeaker transducer within its enclosure in order to develop criteria for designing suitable filters for the improved frequency-dependent excursion limiting circuit of the invention.
Such measurement techniques have been practiced in connection with the prior art circuit of FIG.
3 described herein.
In FIG.
1, the transducer of a loudspeaker is shown in the form of a cone driver 11.
Also shown is an excursion detector 13 mounted to the front of the cone driver to measure the excursion of the driver's dust cap 15.
The excursion detector is comprised of a bridge member 17, suitably be manufactured of a ¼ inch square metal bar, mounted to the rim 19 of the cone driver by means of stand-off posts 21.
Bridge member 17 carries two low force contact switches 22, 23 having suitable depth adjustments 25 to adjust the position of the contact switches to a position that correlates with the maximum safe travel (excursion) of the driver cone 26.
To provide a safety factor, the contact switch depths are adjusted to a position slightly less than the maximum safe travel (excursion) of the driver cone (suitably 15 to 20 percent less).
The maximum safe travel of the cone can be determined by several parameters, including suspension limits and voice-coil and back-plate collision limits, and need not be symmetrical.
It is seen that contact switches 22, 23 detect movement of the driver cone 26 by means of an L-shaped position-indicating element 27, suitably fabricated from a light-weight rigid material, such as a bent segment of steel wire, which is glued to the loudspeaker dust cap 15 for the purpose of taking the measurements.
When a single frequency tone is applied to the loudspeaker, the voltage at which the position indicator 27 contacts one or the other of the contact switches 22, 23 will be the maximum safe peak voltage of the loudspeaker at the indicated frequency